X-ray images, above all fluoroscopy images, have long been recorded to support interventional procedures, and this includes puncturing. The problem arising with puncturings is that very frequently the targets of the puncturing (such as gallstones or tumors) cannot be recognized at all on the x-ray images. The physician performing the treatment must thus basically use the skeleton of the patient for orientation. The practice of recording three-dimensional image data sets beforehand and registering these images with the x-ray system is known. The term registration means that the coordinates which apply for the three-dimensional 3D image data set are assigned to the coordinates of the x-ray system such that a mapping of the one coordinate system to the other coordinate system is defined (correct positional and dimensional assignment of the coordinates). The images from the one system, i.e. the images recorded beforehand, can then be assigned to the x-ray images recorded afterwards. The two-dimensionality of the x-ray images recorded afterwards requires them to be recorded from a specific perspective. Now, on the basis of the registration, i.e. as a result of the correct positional and dimensional assignment of the coordinates, a 2D image representation which assumes precisely this same perspective can now be created from the three-dimensional image data set. Then the two images, i.e. the recorded x-ray image and the computed 2D image can be overlaid. As with registration, the prior art includes a plurality of technologies for doing this. This method is preferably used for puncturings, with the three-dimensional image data being created with an imaging method in which the puncturing target is easily visible. The registration thus makes it possible for the puncturing target to be incorporated into the x-ray image that the physician records during the puncturing. This makes it possible for them to orient themselves during the puncturing.
The problem which arises with puncturing however is that the puncturing needle is almost one-dimensional. The needles are visible as line-shaped objects in the x-ray images. Not visible in this case is whether the needle in the direction perpendicular to the image plane is located in front of or behind the puncturing target, or whether it is actually pointing at the puncturing target. In a fluoroscopy image recorded from the side it is thus not possible to check in the plane perpendicular to the image plane whether the needle is located at the correct point.
It is not possible during a puncturing to record an image of the needle from above such that the image plane lies perpendicular to the extent of the needle, since then the physician's hands would come into the image which would involve a radiation risk to the physician.
A stereo x-ray apparatus is known from DE 36 23 082 A1 in which a puncturing needle is aligned in a holder before intervention into a patient. Sensors in the holder determine to position of the holder and calculate a target line of the puncturing needle from this. A target point at which the puncturing needle is currently pointing is then calculated for the stereo images. A target marking is then inserted in the stereo image at the location of the computed target point.
The arrangement disclosed in DE 36 23 082 A1 has however evidently not entered widespread use for a wide variety of reasons.